They're using a Mac friendly engine (Havok) but I doubt the extra development costs (extra programmers, debuggers, QA staff) would be recouped especially when you consider patches and expansions. There would have to be a significant number of Mac subscribers (no current PC players changing to Mac don't count as that is 0 net profit other than the initial purchase of the Mac version) to support it otherwise it would be being paid for by PC and Console subscriptions and generating no profit of its own. I have a feeling if you isolated WoW's Mac version (Mac only subs compared to initial and continued Mac dev costs for patches and expansions) it would be lucky to be breaking even.